1. Field of the Invention
The present invention relates to an apparatus for detecting the presence or absence of a semiconductor wafer or other type of substrate, such as liquid crystal glass substrate, at a station in equipment for processing the substrate.
2. Description of the Related Art
A wet station typically comprises one and more baths filled with DI water or chemicals, and a substrate guide to supply a plurality of substrates to the baths. The substrates are cleaned while being moved sequentially among the baths. Also, a light-sensing unit is installed on each bath in order to detect the substrates that enter and leave the bath. The light sensing unit comprises a light emitting element and a light-receiving element disposed at opposite sides of the bath.
One conventional apparatus for detecting the semiconductor wafer in a semiconductor wet station is disclosed in Korean Laid-Open Utility Model No. 1999-0038610. The semiconductor wet station is constituted by a chemical bath and a de-ionized water bath to remove alien substances from the wafer. The semiconductor wet station also comprises a wafer detecting unit capable of detecting the wafers that enter and leave the chemical bath and the de-ionized water bath. The wafer detecting unit includes light-emitting and light-receiving elements disposed on the bottom of side walls of each bath.
These light-emitting and light-receiving elements of the wafer detecting apparatus are oriented to detect only the presence or absence of semiconductor wafers that are disposed upright at the bottom of the bath. That is, the conventional wafer detecting apparatus cannot detect for the presence of material lying on the bottom of the baths even though it is installed on a bottom portion of the bath.
Another conventional apparatus for detecting semiconductor wafers at a wet station is disclosed in Japanese Laid-Open Patent Publication No. 2000-124293. The wet station comprises a process vessel having transparent sidewalls. The apparatus for detecting semiconductor wafers includes a light sensor installed on the sidewalls of the process vessel, the sensor being oriented to detect for the presence of the upright wafers in the vessel.
However, the conventional wafer detecting apparatus can not detect wafers or damaged parts thereof that remain at the bottom of the process vessel. Accordingly, the wet station continues to operate even if wafers or damaged parts thereof remain at the bottom of the process vessel. Thus, wafers continue to be damaged and contaminated by remnants, thereby lowering the manufacturing yield.